Philips: 956C Valve PA Amplifier, 30 watt

This is an unbranded Philips or Steanes model 956C valve PA amplifier - it's very similar to the Philips 956B that I have, which is why I bought it.

The amplifier was unbranded and came from a batch of various types labelled as "Fox Sound Systems" in Sydney, Australia. I suspect that Fox was an installer rather than a manufacturer, as I haven't found any evidence of them producing equipment—they don’t seem to exist as a brand. It’s possible that this was part of a government contract, as these amplifiers were commonly used in the public school system.

PHILIPS / STEANS SOUND SYSTEM 956C VALVE PA HEAD

VALVE LINE-UP 

1 x EF86

1 x 6N8

1 x 12AX7

2 x EL34

GZ32 Rectifier

INPUTS / OUTPUTS / CONTROLS

Inputs:          Pickup & Microphone 

Controls:      PU Volume, Mic Volume, Bass & Treble 

Output:        Speaker binding posts / banana plug

TRANSFORMERS

Power transformer:   A&R, Type 1687B 

B+   I'm guessing it's about 420 or so volts.  

Output transformer:  A&R, Type 2503

Output impedance:  300, 150, 100, 75, 15

Looks pretty clean inside - likely has not been worked on.  Apart from the odd wax capacitor, I can't see any glaring issues.  

Part of the reason that I like these, is that there's a decent amount of room to work with inside the chassis and it has a few options on the back for things like adding a power switch and speaker jacks.

Not sure what's going on with the impedance selector and the speaker output posts.   It's not a standard set-up, I need to trace the circuit.

Valves are mainly Miniwatt, made in Great Britain, Holland and Australia.  A couple of Japanese EL34s - which I was initially a little disappointed to see, until I read that they're Matsushita valves, made on Mullard machinery and sound the same as the European Mullards.

GUITAR AMPLIFIER CONVERSION

I rebuilt it to resemble the EF86 channel of the Matchless Phoenix—similar to a DC30 but with EL34s. Why? The valve lineup was already similar, the number of knobs matched, and I liked the look of the circuit.  It turned out to be a great decision because I’m really happy with the result.

The signal path is as follows:  Vox EF86 preamp > rotary switch with a variety of capacitor values > volume pot > 12AX7 long tail phase inverter > master volume / treble cut > power valves